A technique for detecting, based on an audio signal, an abnormal sound emitted by a machine such as a fan, a motor, or a compressor has been proposed. In this technique, filtering is executed on a signal received by a microphone, an envelope signal that is based on the filtered signal is generated, and a cross-spectrum of the envelope signal and the received signal is generated.
In the vicinity of a target object to be subjected to abnormality detection, another object that emits a periodic sound may exist. In this case, an audio signal collected via a microphone includes not only a sound emitted by the target object but also the sound emitted by the other object. As a result, the target object may be erroneously detected to have an abnormality due to the sound emitted by the other object.
The following is a reference document.    [Document 1] Japanese Laid-open Patent Publication No. 9-43283.